The invention concerns an aluminium casting alloy, in particular an aluminum diecasting alloy.
Diecasting technology has today developed to the point where it is possible to produce castings to high quality standards. The quality of a diecasting, however, depends not only on the machine setting and the process selected, but largely also on the chemical composition and structure of the casting alloy used. The latter two parameters are known to affect the castability, the feed behavior (G. Schindelbauer, J. Czikel "Mould Filling Capacity and Volume Deficit of Conventional Aluminium Diecasting Alloys", Giesserieforschung (Foundry Research) 42, 1990, page 88/89), the mechanical properties and--of particular importance in diecasting--the life of the casting tools (L. A. Norstrom, B. Klarenfjord, M. Svenson "General Aspects on Wash-out Mechanisms in Aluminium Diecasting Dies", 17th International NADCA Diecasting Congress 1993, Cleveland Ohio).
In the past, little attention has been paid to the development of alloys which are particularly suitable for diecasting high quality castings. Efforts were mostly concentrated on the refinement of the diecasting process technology. Manufacturers in the automotive industry, however, are increasingly demanding the provision of weldable components of high ductility in the diecasting process, and with high production numbers diecasting is the most economic production method.
Due to the refinement of diecasting technology it is possible today to produce weldable and heat treatable castings of high quality. This has expanded the area of application for diecasting components to include safety-relevant components. For such components normally AlSiMg alloys are today used, as these have good castability with low mold wear. In order to be able to achieve the required mechanical properties, in particular the high elongation at rupture, the casting must be subjected to heat treatment. This heat treatment is required to form the casting phase and thus achieve a tough rupture behavior. Heat treatment normally means solution heat treatment at temperatures just below the solidus temperature, with subsequent quenching in water or another medium at temperatures &lt;100.degree. C. The material treated in this way only has a low elongation limit and tensile strength. In order to raise these properties to the required value, artificial ageing is then performed. This can also be process-related, e.g. by heat application during painting or stress-relief annealing of a complete component assembly.
As diecastings are cast close to the final dimensions, they usually have a complex geometry with thin walls. During solution heat treatment, and in particular in the quenching process, distortion must be expected which can require retouching, e.g. by straightening the casting, or in the worst case can lead to rejection. Solution heat treatment also incurs additional costs, and the economic efficiency of this production could be improved substantially if alloys were available which fulfilled the required properties without heat treatment.
AlMg alloys are also known which are characterized by high ductility. Such an alloy is disclosed for example in U.S. Pat. No. 5,573,606. However, these alloys have the disadvantage of high mold wear and cause problems on removal from the mold, which reduces productivity considerably.